This disclosure pertains to an improved process for hydroformylating an olefinically-unsaturated compound to produce one or more aldehyde products.
It is well known in the art that aldehydes may be readily produced by reacting an olefinically unsaturated compound in the liquid phase with gaseous carbon monoxide and hydrogen in the presence of a metal-organophosphorus ligand complex catalyst, and that preferred processes involve continuous hydroformylation and recycling of a solution containing a Group VIII-organopolyphosphite ligand complex catalyst. Rhodium is a preferred Group VIII metal. Such art is exemplified in U.S. Pat. No. 4,148,830; U.S. Pat. No. 4,717,775; and U.S. Pat. No. 4,769,498. For the purposes of this document, such processes are hereinafter referred to as “liquid phase” processes. Aldehydes produced by such processes have a wide range of utility, for example, as intermediates for hydrogenation to aliphatic alcohols, for amination to aliphatic amines, for oxidation to aliphatic acids, and for aldol condensation to produce plasticizers. The process normally produces a mixture of branched and unbranched isomeric products.
The art recognizes that normal or unbranched aldehydes generally provide more value than their iso- or branched isomers. Additionally, it is known that the ratio of normal to branched isomers is a function of carbon monoxide partial pressure, and typically lower carbon monoxide partial pressures give products with higher normal to branched ratios. Rhodium-organopolyphosphite ligand complex catalyzed liquid phase processes have been shown to give very desirable normal to branched isomer ratios.
Heterogeneous versions of homogeneous catalyst systems are very common. Generally, a heterogeneous analog is less active and selective but offers the advantages of easier catalyst/product separation and better heat removal. Much work over the years has been carried out to develop a viable heterogeneous hydroformylation catalyst. The early catalysts were supported metal oxides, such as rhodium, on silica as reported in U.S. Pat. No. 3,352,924, U.S. Pat. No. 4,185,038, U.S. Pat. No. 4,361,711, U.S. Pat. No. 4,386,013, U.S. Pat. No. 4,456,694, and U.S. Pat. No. 5,409,877. These catalysts were typically non-selective in terms of normal to iso (n/i) aldehydes and generated high levels of hydrocarbons due to hydrogenation Immobilized hydroformylation catalysts are reported in U.S. Pat. No. 3,847,997, U.S. Pat. No. 4,487,972, U.S. Pat. No. 4,098,727, U.S. Pat. No. 4,045,493, U.S. Pat. No. 4,504,684, U.S. Pat. No. 5,093,297, and U.S. Pat. No. 4,144,191. In these cases, the hydroformylation catalysts are bonded to the support, such as a resin, through some type of anionic or acid/base bonding. Generally, this type of catalyst is used in a liquid phase reaction as a slurry. Although good activity and selectivity can be obtained, the catalysts leach the metal into the reaction liquid over time, rendering any catalyst/product separation advantage moot. An alternative approach is to tether a ligand to a support/resin. The tethered ligand/resin is then reacted with a metal complex to form a bound metal-ligand catalyst precursor as reported in U.S. Pat. No. 5,789,333, U.S. Pat. No. 6,544,923, U.S. Pat. No. 6,121,184, U.S. Pat. No. 6,229,052, U.S. Pat. No. 6,362,354, U.S. Pat. No. 6,369,257, U.S. Pat. No. 6,380,421, and U.S. Pat. No. 6,437,192. Leaching of the metal is also a problem with tethered catalysts. U.S. Pat. No. 6,229,052 and U.S. Pat. No. 6,369,257 disclose using rhodium/grafted polymers as fixed bed vapor phase catalysts for hydroformylating propylene. The vapor phase catalyst gave results similar to the slurried version, albeit with lower conversion and activity. Significant activity decline was also observed with the vapor phase catalyst.
Accordingly, it would be desirable to have a gas phase hydroformylation process that would be able to maintain substantially stable activity over time compared to the processes of the prior art.